Primary pulmonary hypertension is a rare disease characterized by increased pressure in the vessels of the lungs. Currently, it is not clear what causes PPHTN. The incidence of this disease is estimated around 2 cases per million in the population. Females are slightly more at risk than male (with a ratio of about 1.7:1). In most patients, the disease is first recognized in their 30's and 40's, although PPHTN can occur anytime from infancy to greater than 60 years of age. The most common symptom is dyspnea, the sensation of shortness of breath. Progressive worsening of the disease can lead to heart failure and eventual death.